Metal Matrix Composite (MMC) materials comprising a ceramic fibre such as silicon carbide fibre, and a matrix comprising a metal are known. For example, one known MMC material is titanium Metal Matrix Composite (TiMMC), in which the fibre comprises silicon carbide (SiC), and the composite comprises a metal such as titanium alloy (Ti6Al4V). Other MMC systems are known. For example, the ceramic fibre may comprise alumina or sapphire, and the metal may comprise aluminium or aluminium alloy.
One application for TiMMC materials is reinforcement for “blings”. Blings are integrally formed bladed rings, comprising a ring and a number of radially extending aerofoils. Blings are used to form compressor stages in gas turbine engines. However, in order to provide the necessary strength, the blings must in some cases be reinforced by reinforcement rings comprising TiMMC.
The silicon carbide fibres are generally formed using a Chemical Vapour Deposition (CVD) process, in which SiC is “grown” on a carbon or tungsten core. A carbon or carbon rich coating may then be applied to the surface of the SiC fibre to prevent chemical reactions between the titanium alloy and SiC during the consolidation process. The SiC fibres are then coated with a titanium alloy in a Physical Vapour Deposition process (PVD—also known as “sputtering”). An alternative, though less commonly used method comprises Electron Beam Physical Vapour Deposition (EBPVD).
The coated fibres are then wrapped around a shim placed between a pair of circular metallic plates. The shim provides a spacing between the plates, such that the spacing is approximately the same distance as the diameter of the coated fibres. Once the required number of layers is wrapped around the shim, the coated fibres are consolidated by, for example, vacuum hot pressing or hot isostatic pressing (HIP), to form a solid article such as a preform or composite disc. However, in order to maintain the spacing between the plates to the required tolerance across the diameter of the plates during the wrapping process, the plates have to be extremely flat and parallel, to within a few microns. This makes the plates expensive, and limits the size of article that can be manufactured using his process, as it is difficult to maintain such a tolerance on large diameter discs. Furthermore, since the coated fibres vary in diameter somewhat (generally by up to ±5 microns), the spacing may in some cases by larger than the diameter of some of the coated fibres, to the extent that some of the coated fibres overlap during the wrapping process. In other cases, the diameter of the fibres may be greater than the spacing, such that the fibres may snag and snap as they are wound between the plates.
The present invention describes a method of forming a fibre composite article, and an apparatus for forming a fibre composite article which seeks to overcome some or all of the above problems.